The present invention relates to cryosurgery and more specifically, to a method and system employing three-dimensional ultrasonography for assisting in the placement of cryoprobes and other medical instruments during percutaneous prostatectomy procedures.
One of the most important functions of clinical surgery is the resection and removal of undesirable tissues. Cryosurgery is an alternative surgical technique in which undesirable tissue is frozen, in the hope that freezing alone will destroy the undesirable tissue without necessitating resection and removal of the undesirable tissue. Leaving dead tissue in place may have beneficial immunological effects.
Cryosurgery is performed using one or more internally cooled cryosurgical probes which will be hereinafter referred to as cryoprobes. A typical cryoprobe is a surgical device having the general appearance and size of a conventional knitting needle, which is provided with cooling sites disposed at predetermined locations on the outer surface thereof. Typically, the cooling sites are located at the tip of the cryoprobe and cooling is accomplished by employing one of a variety of cooling means such as boiling of refrigerants, cooling of refrigerants, Joule-Thomson effects etc. In a typical percutaneous transrectal cryosurgical procedure, such as a prostatectomy, the cooling site on the cryoprobe is first brought into contact with the undesirable prostate tissue. The cryoprobe is then cooled and, as the temperature of the probe is lowered, tissue freezing begins from the cooling site surface outward into the tissue forming a frozen region commonly referred to as an ice-ball. Typically, freezing is continued until the ice-ball has encompassed all the prostate and any undesirable tissue known to exist outside the prostate. However, as will be described in greater detail below, up until now, the extent of the freezing is usually approximated by the practitioner. The frozen tissue is left in situ to be dealt with by the body""s immune system.
In contrast, in traditional resection surgery, the practitioner targets the undesirable tissue and using visual and tactile control, manually resects and removes that tissue.
Cryosurgery has numerous advantages which have promoted small scale, steady use of this procedure for approximately 150 years since the first description of the method by J. Arnott in 1845. Arnott taught that, by applying a brine solution to diseased skin tissue, the tissue could be frozen and destroyed. One of the advantages of cryosurgery is the ease with which this procedure can be applied with minimal trauma to the patient. Conventional surgical procedures require resection which results in blood loss and trauma to the patient.
In modern prostate cryosurgery, cryoprobes are inserted into undesirable tissue through small punctures in the skin at predetermined sites, thereby minimizing the surgical trauma experienced by the patient. In comparison, resection surgery of the prostate is considered a major surgery, with significant bleeding, morbidity, mortality and lengthy recovery periods. There are also further risks and side effects associated with resection surgery such as wound infection, urinary tract infection, deep venous thrombosis, impotence and incontinence.
Another advantage of cryosurgery is that the cryoprobes are applied focally, to treat only the undesirable region, thereby sparing much of the surrounding healthy tissue. This aspect of the procedure has found important applications in liver cryosurgery. In resection surgery, the extent of the tissue removed is determined by many considerations related to conventional resection strategy, such as integrity of the blood supply and the functionality of the tissue remaining after surgery. Often, this strategy requires removal of significant amounts of healthy tissue or even whole organs.
In contrast, the strategy of a cryosurgical procedure is to only remove the undesirable tissue, even if it has irregular margins and shape, leaving the healthy tissue intact. Cryosurgery can therefore be considered a tissue-sparing procedure.
Furthermore, after resection surgery it is often very difficult to retreat the tissue if the disease recurs due to severe fibrosis and the risks of damaging either the sphincter, causing incontinence, or the rectum. However, when cryosurgical procedures are employed, the tissue can be, and routinely is retreated because adhesions and fibrosis considerations are not significant factors. Further to this end, because there is less fibrosis and adhesions in the pelvis, cryosurgery is also advantageous over other modern localized treatment modalities such as, radical prostatectomy, hyperthermia or radiation therapy.
The above-described advantages of cryosurgery have helped the method remain in use for the last 150 years. However, while this type of procedure is effective in many situations where a non-invasive procedure is required, there are several disadvantages with conventional cryosurgical techniques.
Many practitioners were reluctant to use cryosurgery because it was considered inferior to resection surgery. The technique suffered from three major drawbacks which rendered it problematic. Firstly, when the cryosurgical procedure is internal and as no large incisions are made, the practitioner does not have tactile and/or visual contact with the undesirable tissue and is therefore forced to operate xe2x80x9cblindxe2x80x9d. Operating xe2x80x9cblindxe2x80x9d severely hinders an accurate determination of the outline of the prostate and the extent of any other undesirable tissue. Accordingly, the determination is, at best, only an approximation, based primarily on the practitioner""s experience and skill. Secondly, due to the lack of tactile and/or visual contact, the ability to control the extent to which the undesirable tissue is being frozen and thereby destroyed is limited and, once again, must be approximated by the practitioner. Furthermore, the third disadvantage of particular relevance to the present invention is that it is typically very difficult to place medical instruments, such as cryoprobes, percutaneously with any comfortable degree of accuracy. Therefore it is possible that inaccurate placement of the medical instruments could lead to over treatment beyond the desired region, leading to detrimental side effects such as incontinence.
Unlike after resection surgery, after cryosurgery, the undesirable tissue remains in the patient at the end of the procedure. After resection surgery, the practitioner takes confidence in the effectiveness of the procedure in question, by virtue of the fact the undesirable tissue was removed from the patient. However, after a cryosurgical procedure, due to the fact that the undesirable tissue is left in the patient, the level of confidence as to the effectiveness of the procedure is low as there is no true knowledge as to whether or not the undesirable tissue was extirpated. In conventional cryosurgery the practitioner has no means for confirming the success of his procedure immediately at the completion of the cryosurgical procedure. This is also disadvantageous to the patient""s psychological state-of-mind, as the patient must recover and wait for further post-surgical testing to determine the effectiveness of the procedure.
The above described disadvantages of cryosurgery were severe enough to make the use of cryosurgery questionable for many years. Probably the most significant breakthrough in cryosurgery occurred when body imaging technologies were developed, and two-dimensional ultrasonography was employed to image the freezing process during cryosurgery. The use of two-dimensional ultrasonography has resolved in part the original drawbacks with cryosurgery and has led to an unprecedented growth in the use of this technique. However, while the use of two-dimensional ultrasonography imaging has alleviated some of the practitioner""s above- described visual disadvantage, two-dimensional ultrasonography has not completely resolved the imaging problem. Furthermore, two dimensional imaging does not significantly increase the practitioner""s ability to control the extent to which the undesirable tissue is being destroyed in the patient.
Accordingly, there has been a long standing need for an improved method and system, employing three-dimensional ultrasonographic imaging, for assisting in guiding and placing medical instruments during percutaneous prostatectomy which overcomes at least one of the above-described disadvantages of conventional cryosurgical techniques.
It is an object of the present invention to provide a novel system and method for assisting instrument guidance and placement during a percutaneous cryosurgical prostate therapeutic procedure which obviates or mitigates at least one of the disadvantages of the prior art methods.
According to one aspect of the present invention, there is provided a method employing a three-dimensional ultrasonographic imaging system for determining the placement position of at least one medical instrument in a prostate during a prostate therapeutic procedure, comprising the steps of: i) positioning a reference means relative to a ultrasonographic transducer in a region proximal a site on a patient which facilitates access to the prostate; ii) minimizing relative movement between the reference means and the site; iii) referencing the reference means to the three-dimensional ultrasonographic imaging system to determine the spatial relationship therebetween; iv) obtaining a three-dimensional image of the prostate; v) via a processing means, generating a positioning image by superimposing an image of the reference means over the three-dimensional image; vi) from the positioning image, selecting a target location within the prostate where the at least one medical instrument is to be placed; vii) from the positioning image, determining an insertion path to the target location and determining placement coordinates from the image; and viii) placing the at least one medical instrument into the prostate along the insertion path via the placement coordinates determined from the positioning image.
Steps i) through viii) may be repeated for a plurality-of medical instruments.
Preferably, the method includes an additional step, concurrent with steps vi) and vii), of indicating and inputting to the processing means, via a graphical user interface, the target location and insertion path over the positioning image.
Preferably, in accordance with the method of the present invention, the method includes a further step, concurrent with step viii), of monitoring placement of the at least one medical instrument along the insertion path to the target location, via the placement coordinates, with one or more images generated by the three-dimensional ultrasonographic imaging system.
According to another aspect of the present invention there is provided a method of assisting placement of at least one surgical instrument in a prostate during a cryosurgical prostatectomy, comprising the steps of: i) positioning a reference plate relative to a transrectal ultrasonographic transducer in a region proximal a site on a patient which facilitates access to the prostate; ii) securing the reference plate to minimize relative movement between the plate and the site; iii) referencing the reference plate to a three-dimensional ultrasonographic imaging system to determine the spatial relationship between the transrectal ultrasonographic transducer and the plate; iv) obtaining a three-dimensional image of the prostate; v) generating a positioning image by superimposing an image of the reference plate over the three-dimensional image; vi) from the positioning image, selecting a target location within the prostate where the at least one medical instrument is to be placed; vii) from the positioning image, determining a path to the target location via the image of the reference plate and determining placement coordinates from the image; and viii) placing the at least one surgical instrument into the prostate via the reference plate at the placement coordinates determined from the positioning image.
According, to another aspect of the present invention there is provided a system, employed in combination with a three-dimensional ultrasonographic imaging system, for assisting in the placement of at least one medical instrument into a prostate comprising: a reference means; a mounting means for mounting the reference means in a predetermined relationship to a transrectal ultrasonographic probe; the reference means including a plurality of apertures arranged in an predefined manner and sized to permit a medical instrument to pass therethrough; a processing means for determining the spatial relationship between a three dimensional ultrasonographic image of the prostate generated via the transrectal ultrasonographic probe and the reference means; wherein the processing means merges a representation of the plurality of apertures with the three dimensional ultrasonographic image to assist in the placement of the at least one medical instrument in the prostate via an appropriate aperture.
Preferably, in accordance with the system of the present invention, the predefined manner of arranging the plurality of apertures forms a Cartesian coordinate grid.
Alternatively the predefined manner of arranging the plurality of apertures is a polar coordinate grid.
Also preferably, in accordance with the system of the present invention, the mounting means is attached between the transrectal ultrasonographic transducer and the reference means.
Also preferably, the reference means comprises a transparent rectangular plate which is contoured on one side to closely fit a patients perineum.
Also preferably, in accordance with the system of the present invention, the plurality of apertures are provided with an index marking scheme to assist in the identification of placement coordinates and the selected aperture.
Also preferably, in accordance with the system of the present invention, the mounting means includes a transverse adjustment means for adjusting the reference means transversely relative to a long axis passing through the transrectal ultrasonographic transducer.
Also preferably, in accordance with the system of the present invention, the at least one medical instrument is a biopsy needle.
Also preferably, in accordance with the system of the present invention, the at least one medical instrument is a guidance sheath.
Also preferably, in accordance with the system of the present invention, the at least one medical instrument is a cryosurgical probe.
Also preferably, in accordance with the system of the present invention, the processing means forms an integral portion of the three-dimensional imaging system.
Also preferably, in accordance with the system of the present invention, the processing means is a stand-alone computer.